Sighting mechanism



April 19, 1949.Y

3 Sheets-Sheet 1 Filed Sept. 26, 1942 b WM?, E W5 Attorneg April 19, 1949. F. v. JOHNSON SIGHTING MEGHANISM 3 Sheets-Sheet 2 Filed Sept. 26, 1942 nventor: Frth'io? Johnson 9 big Fig? slm April 19, 1949. F. v. JoHNsoN SIGHTING HECHHISM O n....hn O

3 Sheets-Sheet 3 Fig. n;

Filed Sept. 26, 1942 ITK/.STTSZOVT' F`r`ithiof` V Johnson, b9 v J/WW His Attorney.

Patented Apr. 19, 1949 srcn'rmc MncnANrsM Frithiof V. Johnson, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application September 26, 1942, Serial No. 459,780 i Claims.

This invention relates to sighting mechanism, more particularly to sighting mechanism for use in the control of gunfire, and it has for its object the provision of improved mechanism of this character.

While it is applicable more generally in the control of gunnre, this invention is especially useful in the control of the fire of machine guns mounted on rapidly moving supports, such -as aircraft. And it contemplates the provision of improved sighting mechanism `for introducing corrections into the line of iire of the gun so as to compensate for certain factors, such as the speed of the target.

In accordance with this invention, a sight is provided for establishing a line of sight to the target. The sight is mounted upon a support which is movable so that the line of sight may be brought to bear on the target and follow it. The support is caused to move in a rigid system with the gun which is controlled.

Also mounted upon the support is a gyroscope which is free to move about a predetermined point of suspension. The gyroscope is coupled to the support so that these members may be moved relatively to each other, but the coupling means is constructed and arranged to apply a torque to the gyroscope which is proportional to the magnitude of the displacement between the gyroscope and the support and which tends to precess the gyroscope to bring its spin axis into a predetermined position with reference to the support. When the support is moving in order to cause the line of sight to follow a target, the gyroscope spin axis will be displaced from this predetermined relative position by an amount dependent upon the speed of the support, that -is, the velocity of the target, and also upon the strength of the coupling means between the gyroscope and support.

The strength of this coupling means is controlled in accordance with 'ballistic characteristics of the gun to determine the correction to be applied to the line of re of the gun as it is related to the line of sight to the target. Thus, in order to give the gun the correct lead," that is, yto give its line of fire the correct direction in advance of the line of sight, as is made necessary by, the speed of the target, to cause the projectile iired by the gun to arrive at the same 2 position in space as the target and at the same instant of time in order to score a hit, the

strength of the coupling means is controlled in accordance with the time of :flight of the projectile from the gun to the target.

Therefore, the device measures the apparent angular velocity of the target and utilizes the time of ilight of the projectile to compute the correct lead angle for the gun.

For a more complete understanding of this invention, reference should be had to the accompanying drawings in which Fig. 1 is a vertical elevation of sighting mechanism arranged in accordance with this invention, parts being shown in section so as to illustrate certain constructional details; Fig. 2 is a horizontal sectional view taken through a part of the apparatus shown in Fig. 1; Fig. 3 is a sectional view taken through the line 3-'3 of Fig. 2 and looking in the direction of the arrows; Fig. 4 is an elevation, partly in section, of the gyroscope used in the apparatus shown in Figs. 1-3 and also illustrating certain control elements therefor, this ligure being drawn to a' larger scale than Figs. 1-3; Fig. 5 is an expanded perspective view illustrating certain apparatus used to control the operation of the gyroscope of Figs. 1-4; Figs. 6 and 6a are diagrammatic representations of the eld of battle; Fig. 7 is a diagrammatic representation of certain control means for the gyroscope; Fig.

' 8 represents an aircraft provided with a machine gun which is controlled by the sighting mechanism of this invention; Fig. 9 is a vertical central sectional view taken through apparatus arranged in accordance with this invention, but illustrating an embodiment of the invention dierent from that shown in Figs. 1-5; Fig. 10 is a sectional view taken through the line lll- I0 of Fig. 9 and looking in the direction of the arrows; Fig. 1l is a sectional view taken through the line lI-H of Fig. 9 and looking in the direction ofthe arrows; and Fig. 12 is an enlarged sectional view of certain control elements for the gyroscope.

Referring more particularly to Figs. 1-8 inclusive, this invention has been shown in one form in connection with a sighting device i0 (Fig. 8) intended to be used in the control of a machine gun Il, mounted upon a suitable aircraft i2, and intended to determine for any firing problem the gun lead angle made necessary by the airplane' t2.; 1 :Prefer-ably; it will: he mounted 'outfin greater-fdetaiihereinafter. i Mounted withf-i mounted uponfa fljxed bracket il, mounted in tiie at; right angles to the .suspension axis cfj 1 the :girnba'l is a -eyroscopc :i9 which; ras shown.:

1 scope casing is; a .suitableihigh speed motori (noti shown; which drives' the .fgyroscope' gwheei 1 shaft 1,22 (pag.1 n.f The :axis o'fthe shaft: 22,: ci course: @is =the spin axis of; the igyruscope.=y i 1 krf i1 1 .f 1 1 .The shaft-,22z projects ifi-cm1 the g'yro'scope cafs-i l fing: and! on projecting end fit: 'carries `ari eddy 1 lcurrent :disk-'23; 1 'lhei eddy current disk 123 com:

1 ings' an; cuter :curved surface approximately in conducting sheet 26, which preferably will be made of copper.

, Positioned opposite the eddy current disk 23 is a suitable electromagnetic device 21 xedly mounted in the adjacent wali of the casing i 3. The magnet 21 comprises a central pole 28 and an outer annular pole 29. Inserted between the poles is the magnet energizing coil 30. The winding 30, as shown, is held in place by means of the outer polevpiece 29.

The magnet 21 is mounted in the casing I3 so that the longitudinal axis of the central pole piece 28 passes through the center of suspension of the gryoscope; and the lengths and shapes of the pole pieces 28 and 29 are such that their ends lie on a spherical surface having its center Vat ,the center of suspension of the gyroscope.

The magnet 21 and eddy current. disk 23 constitute a coupling between the gyroscope and lthe casing I3 which applies a torque to the gyroscope which tends to precess it into alignment with the axis of the magnet.

Here it should be noted that theV magnet is positioned so that its axis is in alignment with the gun.

It will be understood that in the operation of the coupling between the casing I3 and the gyroscope, when the eddy current disk 23 is rotating in the magnetic field set up bythe magnet A21, and the axis of the gyroscope is aligned with the axis of the magnet, no eddy currents are induced in the disk. However, if the axis of the magnet departs from the axis of the disk, the motion' of the disk under the magnets poles yaccepteer i the. relative speed ofthetargetf In this :specific f :,rapplication, the gun il :is nxedwith-,reiaticn tu 1 the plane. I2.. 3 fln'other words, itis notimounted 1 1 1 z 1for`r movement relative to the' fplane itself.k 1 :its 1 1 position :in spacetofdirect itslneo fireisde-fA :1;1f1;1;1;-;1f1;111e1;1eterminedsoieiybythefpositionot the airplane@ 1 1 1 land with the coemcient of coupling,l 'whichl isa' 1 11 evice 1 in: comprise la metallic 1 1 f :casing 1li which f also; is ixed with reference to f 1 `l01 1 onder the cowl or scmeetherf outcf=the-way 1 1 location; but `it fmustbevso. positioned lthat zthe opticaisighting; element of; the deviceisf projectedg f 1 linto the 'pilots held off View, as .will be pointed p in lthecasing i 3 isa :,gimbgal 1&4 whichis .supportedy 1 .byf a pair-10i: shafts; i5 :and 1 i3 to rotate-y upon, zo.: 1 f normally; horizontal axisf 1 :The shafit 1511's faxed to one wall; ofz the casing; while; theshaft iis: 1 1

.Casina f .The rias f i4 is :provided withiba11=bear1 1 ings :I8: mounteciupon these fshatts :151 :and iti i 1 Pivotedi to :the gimbal ring I I3 to move -f about: an

1 is 1 provided on opposite sides; with hail bearings 1 201 which; are .,:Eournaied :m1 shafts yt li carried hy 1 .the fgirihaiy ring 1I4; 1 ;Mounted1withinthe fgy-ro.a s

` 1 :prises ;a:steei =clsk124f which 'isr keyed to tlieshatt 1 l ft2 and which-carriesia second steelipiate 215 hav-1 1 s the forrnf of a segmenti oi. a sphere which has its; 1 i

fc scope.l -Spun' over' this surface is lan electrically 4 causes eddy `currents to fowi in thecop'per' sheet 1 f 1 :26; 1, A resulting electromagnetic force facts :on the 1 f gyrnsccpe ,which tends: to lprecess it into align- 1 1 1 .ment withfthef magnetic. axis.l 1 .Thefmagnltude of 1 1 f 1 lthis `force varies approximateylinearly with the 1 I i s angler :between 1' the I gyroscope andi the? :magnetik i l i function 'of the magnet; excitaticuicurrent.1r This I i s excitation offthe; magnetic contr-oiled ibymearxsl of 3a suitable -rheostat :3l 1 connected 'in i the circuiti of? 1 themagnetr andi controlled bye manuaily oper-i l 1 =able-knnhtZz(scenes:iaiidi').l -f 1 i 1 1 1 1 j 1 j ffhe :gy'oscop'controls =the 'direction fof? the l 1 1 1 line ofsi'ght lofi the device in accordance withj f f f theidispiacementr of its spin axis with reference' l f .t0 fthe casing i i3.. The optical 'systemy controlled? 1 1 1 by the gyrosecpe :is constructedand arrangedk to 1 1 estabich1acoilirnatediinecfsight; and. the gyra@ 2 f 1 `sgccjpefis connected to operate amovalbleeiement 261 inf the1system1-f This movable elettroni:1 is .a1 reti :cula 353.; #The reticue- 33 may have any suitable iormf,: but f preferably will 'ini l,the torni oi cir--= 1 k cular 1 glass with; una :sllveredside in which; a f 1 f fsuitable cross,mark is scribed, the cross-'mark l 1 simulating cross-hairs.y 'Thefreticule glass' 1331s: 1

7rndunteii ;in1 fa: suitable cylindrical: supper-tf 331 with the; silvered side out.: .The tubelori cylinderf 1 fet is provided .at 1its f end; 'opposite the reticule -f 1 1 fgiass; with la :spherical beliedi -mouth1 35.-y 'This f i fbgeiled; mouth fis; pivoted: vin .a dork-like extension f i351 org the fgmbal ring Meer that. it moves 'onen-11l f .ax-is; parallel with :the axis i of. movement lof the -gyrcscope casing; in: this gimbai ring.= As showin,= f g ,the boiled section 3.5 provided 1with oppositely protruding shafts a 381 which are 1 received -fiucflziear-S 1 -1ings:39;providediforzthem-intheicrlted1-end if p Sigi-ofthegimbalring; It is to be understood that; the. axis: of; suspension ot the bejlied :mouth f 35 passes through; the center f of the 1, spherical boli.1 o f'lhe.reticule= holder; tgisfalso connected tothe mii: 1 -gyroscope easing'lby means ofv a 11ink39a for lin'r-A 1 parting to the longitudinal axis of the support 34 the same motion that the gyroscope has about its axis of suspension in the gimbal ring I 4.

It will be observed, therefore, that in view of the mounting of the reticule support 34 and its connections with the gyroscope the longitudinal or optical axis of this support always will have a fixed relationship to the spin axis` of the gyroscope. In the specific embodiment of the sighting mechanism illustrated, the axis of the tubular support 34 is parallel with the spin axis of the gyroscope. i It is contemplated that the shape of the reticule will be projected into the observer's eld of view as a light image, and for this purpose a source of light 4I) in the form of an incandescent lamp is rigidly mounted in the wall of the casing I3 opposite the open end of the bell 35. As shown, this lamp is mounted in a suitable socket 4I provided forit, which socket is attached directly to the casing.

Interpcsed between the incandescent lamp 40 and the reticule 33 are condensing lenses 42 (Fig. 1). The lenses 42 are mounted in a suitable housing 43 which is mounted in the casing I3. as shown. The end of this housing whichcarries the condensing lenses is spherical in shape, as shown in Fig. 1, and it projects into the belled mouth 35 of the reticule holder 34 to prevent stray light leakage.

The optical system of the sight further comprises a three-lens inverting system 44 xed to the casing I3 so that its optical axis is coincident m `with the optical axis of the reticule support 3M when the spin axis of the gyroscope is coincident with the axis of the magnet 21. In addition, the optical system comprises a 45 reecting prism 45 which directs light rays from the lamp at 90 to the optical axis of the lens inverting system 44 upwardly through a tube 45a. And also comprises a collimating system provided by two collimating lenses 46 mounted in the tube 45a. In addition, it comprises a transparent reflecting glass 41 mounted albove the top collimating lens and which is adjustably mounted upon the upper end of the tube 45a, but which normally is inclined at an angle of 45 to the vertical axis of the sight. It is through this reflecting glass 41 that the observer views the target. It should be noted here that while the casing I3 will be positioned under the cowl or at some out-of-the-way place, as previously pointed out, it must be so positioned that the reflecting glass 41 will be brought opposite the eye of the observer so that he may conveniently view the target eld through this glass. i

It will be understood that in the operation of the optical system, the condensing lenses 42 will collect the light from the filament of the lamp 40 and direct it through the reticule 33 so that it also passes through the inverting lens system 44. The inverting lens system 44 forms an enlarged inverted realimage of the reticule at some plane 41a. Light from this real image is collimated by the two lenses 46 and reflected from the glass plate 41, and the observer will apparently'see the cross-mark intersection of the reticule at iniinity through the glass 41. And he will be able to observe such cross-mark intersection no matter where his eye is located in the exit eld, and no matter how the position of the reticule be shifted by the gyroscope. In other words, if the reticule holder 34 be shifted through an angle 0, all of the rays of light from the cross-mark intersection at the center of the reticule will leave the reflecting glass 41 at the angle 0 from the axis of the sight, so that so long as the observer looks in the direction fixed by these rays he will see the cross-mark intersection. And his line of sight will have been established parallel to the gyroscope axis.

In the operation of the sighting device, the reticule in the eld of view 'of the observer is brought to bear on the target and is held on the target by moving the support I3, that is, by moving the airplane I2. As pointed out previously, when the casing I3 is so moved the axis of the gyroscope will lag behind it by an amount which is dependent upon the speed of the gyroscope and the coupling coeicient between the gyroscope and the casing. The coupling coeiiicient is adjusted by the resistance 3| in accordance with the time of flight of the projectile to the target so that the lag in the position of the gyroscope axis behind the support I3 is the correct lead angle for the gun I I. The rheostat is graduated in terms of range, and preferably a range scale, graduated in hundreds of yards, will be providedto assist the observer in setting the time of night knob 32.

In other words, in the operation of the device the observer directs the plane I2, that is, in effect controls the movement of the casing I3 so as to cause the line of sight to follow the moving target, this in spite of the fact that the reticule 33 itself has been moved in space with reference to the optical axis of the system by the gyroscope which is displaced with reference to the casing I3 in the manner previously described. Therefore, when the reticule image is maintained on the target, the position of the gun II, which in effect is fixed to the casing I 3, necessarily will be advanced with reference to the line of sight through an angle equal to the angie of lag of the gyroscope behind its support, and this angular advance will be the -correct lead for the gun, as required by the speed of the target.

This may be more fully understood by reference to the diagrammatc representation of the eld of battle shown in Figs. 6 and 6a. The sight is assumed to be at the position a and the present position of the target at b.

In discussing these gures, the following factors will be considered:

V--evelocity of target relative to own airplane R=present range of target R=advance range of target y T=time of flight of the projectile corresponding to range R Ta=time of flight of the projectile corresponding to range Ra lii=angular velocity of target about own air-'planey When the angle AB is small, say 10 or less, the difference between it and its sine may be neglected, whence AB RT., dB

IfA the relation between range and time of ight is linear, so that R=KT Ra=KTa which applies regardless of the inclination of the plane containingthe target path and the gun. That is, the angle AB may be in azimuth, elevation, or a combination of both.

This is the relation for the sight. That the sighting mechanism operates in accordance with this relation may be seen by reference to` Fig. 6a.

The coupling coeiiicient, previously referred to,

and to which I give the symbol C, is the precession rate of the gyroscope per unit angle between the amasar The desired relation is'l obtained if from which it will be observed that which is the relationship previously determined.

Therefore, it will be observed that if the coupling coeflicient C is made inversely proportional 'to time night T of the projectile by the range `xheostat 3l, the lead angle of the gun inherently 'is generated, and the gun is directed so that its line of re is advanced by the amount ahead of the line of sight, demanded by the speed of the target. l

It must be noted here that while in the embodiment illustrated the axis of the line of sight is parallel to the spin axis of the gyroscope, this relationship is not necessary. In other words, the line of sight may be non-parallel to the axis of the gyroscope, and in certain conditions of operation it is desirable that it beset in such non-parallel relation. It must, however, be in flxed relation to the! spin axis,

Also, it must be noted that if the gun is not rigidly mounted on the airplane, but is movably mounted with reference to the plane. then the casing I3 must beconnected in a rigid system" to move with the gun.

In a sighting system such as has been described wherein a relatively strong coupling force is generated between the gyroscope and the casing within which it is mounted, any tendency of the gyroscope to nutate becomes greatly magniiied. At times the gyroscope may violently oscillate.

To obviate this, I -have provided a suitable mutation damper. This damper comprises an annular weight rlill which is mounted on the end of the gyroscope casing opposite to the end where the eddy current disk 23 is mounted, and so that its central axis issubstantially coincident with the spin axis of the gyroscope. As'

shown, the annular weight 48 is connected to its adjacent end of the gyroscope by means of a disk-like plate 49 which is spaced from it, as shown. The ring 43 and plate 49 are secured together by means of suitable screws l) and are spaced from each other by means of sleeves 5I surrounding the screws. The disk 49 is secured to the gyroscope casing by means of a stud 52 which is mounted on a plate 53 which in turn is 54 is a suitable resilient gasket or washer Bti formed of any suitable material, such as rubber. and interposed between the opposite side of the plate 49 and the stud 52 is a second resilient washer 56 which may be formed of the same material as the washer 65. Interposed between the resilient washer 5B and the plate 49 are a pair of rigid washers 51 and on the outer side of the washer 56 is a clamping plate 58 which is clamped Iagainst the washer by means of nuts E9 mounted on the stud 52.

In the operation of the damping device, should the gyroscope tend to nutate. the inertia of the weighted annular member 48 will cause the member to fail to follow the rapid movements of the gyroscope. The resulting relative motion between the gyroscope and the annular member will cause an absorption of energy due to internal resistance in the resilient members and 58. and the nutation will be damped.

In the lform of this invention illustrated in Figs. 9-12 inclusive, the gyroscope is utilized to control the position of a telescopic sight, rather than an element of a collimating optical system as in the rst embodiment. Here the sighting mechanism comprises a casing 6l) which is mounted in a rigid system to move with the gun. Mounted within this casing to move on a nor- `xnally horizontal axis is a gimbal ring 6I,` and mounted in this gimbal ring to move on an axis at right angles to its axis of movement is a gyroscope 62. lThe gyroscope is provided with an eddy current disk 63 which coacts with a magnet Gt xed to the casing 60. The gyroscope is provided with a nutation damper 64a. The parts thus far described are constructed and function in the same way as do the corresponding parts of the first form of the invention described.

Here, however, the gyroscope controls directly the movements of a telescope 65 which may be of any suitable type. As shown, the telescope is mounted upon the upper arm of the ring 6I so as to move with it about its axis, and also is connected to the gyroscope to move with it about its ring axis. The parts are .arranged so that the line of sight is parallel to the spin axis of the gyroscope and this axis when aligned with secured to the gyroscope casing in any suitable way, as by screw fastening means 54. This stud 52is positioned so that its longitudinal axis is coincident with the spin 4axis of the gyroscope.

.1 I nterposed4 betweenl the plate M9 and the.' plate the axis of the magnet 64 is in alignment with the guns line of re.

In the operation of the device, the observer will sight the target through the telescope 65. And by the very act of keeping the line of sight `on the target, the observer necessarily introduces the angle of lead to the gun. This is because rthe casing 60 will lead the position of the gyro`I scope by an amount which is proportional to the velocity of the target and which is inversely proportional to the time of ilight of the projectile, all as fully and completely described in connection with the first embodiment of the invention described.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gun sight comprising sighting means for establishing a line of sight, a gyroscope. means connecting said gyroscope to said sighting means so that the direction of said line of sight is maintained in predetermined relation to the spin axis of said gyroscope and is controlled by the position of said gyroscope, means adapted to be moved with the gun for moving said sighting means and gyroscope in space to cause said line of sight to follow a target, a coupling between ,said last-named means and said gyroscope to exert a torque on said gyroscope to tend to cause it to precess to follow said means at is moves to follow said target, and means controlling thel effect of saidv coupling upon said gyroscope in accordance with the time of flight of a projectile from the gun to said target.

2. A system of fire control for a gun comprising sighting means for establishing a line of sight, a gyroscope, means connecting said gyroand said gyroscope for moving them in space so .as to .cause said line of sight to follow a target,

an electro-magnetic coupling between said mount and said gyroscope applying to said gyroscope a precessing torque to cause it to tend to follow said mount, means for angularly moving said gun in space synchronously with said mount, and means controlling said electro-magnetic coupling in accordance with the time of flight of a projectile from said gun to the target so as to measure the lead angle of said gun.

3. In combination with a` gun and mount therefor, means for determining the angle of lead of said gun with reference to the line of sight to a target comprising a support fixed to said mount, a gyroscope mounted on said support for universal freedom of movement about a center of suspension, a sighting device on said support, the line of sight of said sighting device being directed in azimuth and elevation by move-y ment of said support in azimuth and elevation,

connecting means between said sighting device and gyroscope whereby the direction of said line of sight is maintained in fixed relation to the spin axis of said gyroscope and -is varied by the precession movements of said gyroscope with respect to said support, a coupling between said gyroscope and said support for applying a torque to said gyroscope to cause it to precess to tend to follow the movement of said support both in azimuth and elevation in keeping said line of sight on a target, and means for controlling the effective coupling force between said gyroscope and support in accordance with the time of flight of a projectile from said gun to said target.

4. A gun sight comprising sighting means for establishing a line of sight, a gyroscope, means connecting said gyroscope to said sighting means so that the direction of said line of sight is maintained in fixed relation with the spin axis of said gyroscope and is controlled by the position of said gyroscope, means adapted to be moved with the gun for moving said sighting means and gyroscope in space to cause said line of Vsight to follow a target, a coupling between said lastnamed means and said gyroscope to exert a torque on said gyroscope to tend to cause it to precess to follow said means as it moves to follow said target, means controlling the coupling eect of said coupling means on said gyroscope in accordance with the magnitude of a predetermined correction to be applied between the gun.and said line of sight, and means acting on said gyroscope to damp nutation movements set up in the operation of said gyroscope.

5. A gun sighting mechanism comprising a movable support adapted to move with the gun, al target sight including an optical system fixed on said support but having a movable reticule, means for forming an image of said reticule in the target iield of view, a gyroscope mounted on said support for freedom of movement about a l0 predetermined suspension point, means connect ing said gyroscope to said reticule sothat the spin axis of said gyroscope is held in iixed relation to the optical axis of said reticule, a. coupling between said support and gyroscope to apply a torque to precess vsaid gyroscope to tend to follow the movement of said support, means controlling the effect of said coupling upon said gyroscope in accordance with the value of a predetermined correction to be applied to said gun in its relation to the line of sight of said sighting device, and connecting means between said gyroscope and said reticule for shifting its position relative to the optical axis of said optical system in accordance with the displacement of said gyroscope with reference to said support.

6. Gun re control sighting mechanism comprising a support adapted to be moved rigidly with the gun, an optical system on said support including a transparent sighting element through which the target is viewed, the support being moved to bring the target in the field of view of said sighting element, a reticule in said optical system rotatable with reference to the optical axis thereof about a center fixed in said optical system, means for forming an image of said reticule in the field of view of said target, a gyroscope on said support mounted for universal freedom of movement about a point of suspension, means connecting said gyroscope to said reticule so that the spin axis of said gyroscope is held in fixed relation to the optical axis of said reticule, a coupling betweenv said gyroscope and said support applying a torque to said gyroscope to precess it to cause its spin axis to tend to follow the movement of said support, and means controlling the coupling eect of said coupling so as to apply a precessing torque to said gyroscope that has a predetermined relation to the time of flight of a projectile from said gun to said target, and which varies approximately linearly with the angle between the gyroscope and said support. l '7. Gun fire control sighting mechanism comprising a support adapted to be moved rigidly with the gun, an optical system on said support including 'a transparent sighting element through which the target is viewed, the support being movable to bring the target in the field of view of said sighting element, a reticule in said optical system rotatable with reference to the optical axis thereof about a center fixed in said optical system, means for forming an image of said reticule in the field of view of said target, a gyroscope on said support mounted for universal freedom of movement about a point of suspension, means connecting said gyroscope to said reticule so that the spin axis of said gyroscope is held in fixed relation to the optical axis of said reticule, means carried by said support to set up a magnetic field that is symmetrical about said spin axis, an electrically conducting plate carried by said gyroscope for rotation in said spin axis and having the form of a segment ofa sphere with its center of curvature in said point of suspension, the plate being in inductive relation with said magnetic field so that a torque is applied to said gyroscope to precess it to cause its spin axis to tend to follow the movement of said support in causing said sighting element to vfollow a target, and means for controlling the strength of said magnetic field in accordance with the time of iiight of a projectile from said gun to said target.

8. A gun sight comprising a means for estabasomar *f 11 lishing a direction lineto a target, a gyroscope, a connection between said gyroscope and said means for maintaining said direction line in substantially parallel relation with the spin axis of said gyroscope, a common support for said means and said gyroscope movable in synchronism with said gun to cause said direction line to follow a target, and a coupling between said support and said gyroscope exerting a torque on said gyroscope which varies with the angular velocity of said support in following said target so that said direction line is displaced with reference to said gun in proportion to said angular velocity.

9. In a predictor gunsight, means for dening a sighting line, a gyroscope, operative connections from said gyroscope to said means to move the latter and control the direction of the sighting line with respect to the spin axis of said gyroscope, support means, and means whereby said gyroscope is actuated to constrain its spin axis to follow angular movement of said associated support means with a lag which indicates the required deflection angle, said last named means including an electrically conducting member oil'- set along the spinning axis of the gyroscope and operatively connected with the gyroscope to spin therewith and a magnetic member movable with the support means and normally aligned axially with said electrically conducting member, said members cooperating to set up an eddy current drag in said electrically conducting member which exerts a precessing couple about an axis perpendicular to the gyroscope spin axis when the axes oi' said electrical conducting and magnetic members become disaligned.

10. In a predictor gunsight. adjustable means for denning a sighting line. a gyroscope having a spindle, means operatively connecting said spindle to said adjustable means for actuating the same, an electrically conducting member mounted on said spindle to spin with the gyroscope and offset along the spin axis o! the same. gun means. and a magnetic member mounted to move with said gun means and normally aligned axially with said electrically conducting member to set up eddy currents therein whereby the rotation of said gyroscope spin axis is opposed by eddy current drag giving rise to a couple about an axis perpendicularv to the gyroscope spin axis when the axes ot said electrically conducting and magnetic members become disaligned, therby causing said spin axis to precess to follow angular movement oi' the gun with a lag which varies with the angular velocity of movement of said gun and hence represents a variable deectlon angle.

FRITHIOF V. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

